WO2024079439A1

WO2024079439A1 - Method of treating zinc-containing by-product

Info

Publication number: WO2024079439A1
Application number: PCT/GB2023/052560
Authority: WO
Inventors: Owain LLOYD
Original assignee: South Wales Minerals & Mining Ltd.
Priority date: 2022-10-11
Filing date: 2023-10-04
Publication date: 2024-04-18
Also published as: GB202214964D0

Abstract

A method of treating zinc-containing by-product is provided. The method comprises contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11; and contacting the treatment composition with ferrous metal processing by- product comprising zinc, thereby producing a zinc-enhanced solution and a zinc-depleted ferrous metal processing by-product. An apparatus for treating zin-containing by-product is also provided.

Description

METHOD OF TREATING ZINC-CONTAINING BY-PRODUCT

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to the treatment of zinc-containmg by-product. More particularly, but not exclusively, this invention concerns a method of treating ferrous metal processing by-product comprising zinc. The invention also concerns an apparatus for the treatment of ferrous metal processing by-product comprising zinc.

[0002] Steel is typically made by adding scrap steel to molten iron in a process often called the basic oxygen process, or by melting scrap in an electric arc furnace. The scrap steel often has a relatively high zinc content, and the steel making process results in the generation of by-product particles comprising iron and zinc. Such particles are of varying size and zinc content, larger particles often known as “grit” (typically having a lower zinc content), and smaller particles often known as “dust”, typically a free-flowing powder with particles of small size (comprising particles having a mean greatest dimension of 1- 1 OOOmi crons), with a higher zinc content. Such by-product materials (often known as “revert materials”) with a high zinc content cannot be used in a blast furnace. Furthermore, it may be desirable to recover zinc for economic reasons. Zinc may be recovered from the revert materials by thermal processes. One such process is the waelz process, which involves heating the zinc-containing by-product in a rotary kiln with a carbon-containing reductant to a temperature of 1000-1500°C. The zinc is reduced to elemental zinc that is volatised, and then oxidised to ZnO, which is recovered. Another process used to recover zinc is the rotary hearth process. Pelletised material is heated and reduced, with dust containing high levels of zinc being recovered.

[0003] The capital outlay involved in purchasing such thermal processing equipment is high, and the performance of such methods is energy-intensive and expensive, given the heating involved. It is therefore only financially viable to use such methods to treat revert materials with the relatively high zinc content. Revert materials with a zinc content lower than that which is viable to treat is not treated, and is effectively treated as toxic by-product and stored in landfill. It is therefore desirable to develop an inexpensive method for

reducing the zinc content of such materials in order to recover at least some of the zinc and/or so that the zinc-depleted material can be used in a blast furnace.

[0004] In this connection, it is known to treat zinc-containing by-product with acid or alkali to reduce the amount of zinc in the by-product and/or to recover the zinc. Such methods rely on the use of commercially-available acid or alkali, and are therefore relatively expensive.

[0005] The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of treating ferrous metal processing by-product comprising zinc.

SUMMARY OF THE INVENTION

[0006] In accordance with a first aspect of the present invention, there is provided a method of treating ferrous metal processing by-product comprising zinc, the method comprising: contacting a treatment composition with ferrous metal processing by-product comprising zinc, thereby producing a zinc-enhanced solution and a zinc-depleted ferrous metal processing by-product, the treatment composition having a pH of from 8 to 11, the treatment composition having been produced by contacting an aqueous liquid with slag.

[0007] The applicant has discovered that it is possible to use steel slag to generate a treatment composition that may be used to reduce the zinc content of ferrous metal byproduct. The treatment composition dissolves zinc, thereby providing ferrous metal processing by-product with a reduced zinc content.

[0008] The method may comprise producing the treatment composition having a pH of from 8 to 11 by contacting an aqueous liquid with slag, and contacting the treatment composition with the ferrous metal processing by-product comprising zinc. The method may comprise producing the treatment composition having a pH of from 8 to 11 by contacting an aqueous liquid with slag, and subsequently contacting the treatment composition with the ferrous metal processing by-product comprising zinc.

[0009] The method may comprise producing the treatment composition in the presence of the ferrous metal processing by-product comprising zinc. In such a method, the ferrous metal processing by-product comprising zinc is in contact with the treatment composition as the treatment composition is being made. For example, producing the treatment composition in the presence of the ferrous metal processing by-product comprising zinc may comprise reducing the pH of a pre-treatment composition in the presence of the ferrous metal processing by-product comprising zinc. The pre-treatment composition may comprise an aqueous liquid (such as water) and slag.

[0010] The treatment composition may optionally have a pH of at least 8.0, optionally at least 8.5, optionally of at least 9 and optionally of at least 9.5. The applicant has discovered that a pH of at least 9 has been found to be particularly effective at facilitating the removal of zinc from by-product comprising zinc. The treatment composition may optionally have a pH of no more than 11.0.

[0011] The slag may preferably comprise ferrous slag i.e. slag generated during the production of iron or steel. For example, the slag may comprise electric arc furnace slag and/or may comprise blast furnace slag. Ferrous slag optionally comprises one or more of calcium silicate, iron, magnesium and aluminium. Iron, magnesium and aluminium may be in any oxidation state, and may be present in salts.

[0012] Contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11 may comprise contacting an aqueous liquid with slag to produce a pre-treatment composition and reducing the pH of the pre-treatment composition to produce the treatment composition having a pH of from 8 to 11.

[0013] The pre-treatment composition optionally has a pH of at least 11 and optionally at least 12. The pre-treatment composition optionally has a pH of no more than 13.5, and optionally of no more than 13.

[0014] The method may comprise monitoring the pH, optionally monitoring the pH of the pre-treatment composition. The monitored pH may be compared to a desired pH. The desired pH may be, for example, 11 to 13. The method may comprise adding slag or aqueous liquid, dependent on the comparison between the monitored pH and the desired pH. For example, if the monitored pH is greater than the desired pH, the method may

comprise adding water. If the monitored pH is lower than the desired pH, then the method may comprise adding slag. The contacting of slag with the aqueous liquid may be a batch process or a continuous process. The aqueous liquid and slag may be agitated so as to increase contact between the slag and the aqueous liquid.

[0015] The method may comprise monitoring the pH of the treatment composition. The monitored pH may be compared to a desired pH. The desired pH would be, for example, 8 to 11. The method may comprise adding slag or aqueous liquid, dependent on the comparison between the monitored pH and the desired pH. For example, if the monitored pH is greater than the desired pH, the method may comprise adding water. If the monitored pH is lower than the desired pH, then the method may comprise adding slag. The contacting of slag with the aqueous liquid may be a batch process or a continuous process. The aqueous liquid and slag may be agitated so as to increase contact between the slag and the aqueous liquid.

[0016] The treatment composition may be produced in the presence of the ferrous metal processing by-product comprising zinc. For example, a pre-treatment composition as described above may be formed in the presence of the ferrous metal processing by-product comprising zinc, and the pH may be reduced, for example, by providing a pH-reducing agent.

[0017] In this connection, the method may comprise contacting a pre-treatment composition having a pH of greater than 11 with the ferrous metal processing by-product comprising zinc, and reducing the pH, for example, by adding a pH-reducing agent.

[0018] Throughout the present application, a pH-reducing agent may comprise an acid. A pH-reducing agent may comprise a gas, such as a gas comprising carbon dioxide. Such gas may be provided as bubbles, at least a portion of which optionally has a diameter of no more than 500nm, optionally of no more than 400nm, optionally of no more than 300nm, optionally of no more than 200nm and optionally of no more than lOOnm. Such bubbles may be produced, for example, using a Nanobubbler (Fine Bubble Technologies, Cape Town, South Africa). The use of small bubbles is thought to be advantageous in providing a large contact surface area between the bubbles and the ambient liquid.

[0019] The method, and optionally contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11, may comprise contacting aqueous liquid with slag in the presence of a pH-reducing agent. The pH-reducing agent may comprise an acid. The pH-reducing agent may comprise a gas, such as a gas comprising carbon dioxide. Reducing the pH of the treatment composition to produce the reduced-pH treatment composition may comprise passing a gas (for example, a gas comprising carbon dioxide) through the treatment composition. Carbon dioxide reduces pH and produces carbonates that may precipitate. The use of carbon dioxide also facilitates carbon capture in the precipitated carbonates. Those skilled in the art will realise that a gas comprising carbon dioxide may comprise components other than carbon dioxide. For example, air contains carbon dioxide.

[0020] The method may comprise monitoring the pH of the treatment composition. The monitored pH may be compared to a desired pH. The method may comprise changing the contacting of the pH-reducing agent with the treatment composition, depending on a comparison between the monitored pH and the desired pH.

[0021] The method of the present invention may be used to treat ferrous metal by-product comprising particulate. Any suitable size of particulate may be treated, although those skilled in the art will realise that particles of a larger size (e.g. a greatest dimension of 5mm) may be less effectively treated on account of their having a relatively small surface area for the volume of material that is treated. Material treated using the method of the first aspect of the present invention may have a very broad particle size distribution. Optionally, the particulate may comprise a portion of particles having a greatest dimension of no more than 50 microns, optionally of no more than 30 microns, optionally of no more than 20 microns and optionally or no more than 1 Omicrons. Optionally, the particulate may comprise at least 10% by number, optionally at least 20% by number, optionally at least 30% by number and optionally at least 40% by number of particles having a greatest dimension of no more than 50 microns, optionally of no more than 30 microns, optionally of no more than 20 microns and optionally or no more than 1 Omicrons.

[0022] The aqueous liquid is preferably water. Those skilled in the art will realise that any convenient source of water may be used, for example, collected rain water.

[0023] The amount of aqueous liquid may be at least 20wt% of the total weight of the slag and aqueous liquid, optionally at least 30wt%, optionally at least 40wt% and optionally at least 50wt%. The amount of aqueous liquid may be no more than 90wt% of the total weight of the slag and aqueous liquid, optionally no more than 80wt%, optionally no more than 70wt%, optionally no more than 60wt% and optionally no more than 50wt% of the total weight of the slag and aqueous liquid. The amount of aqueous liquid may optionally be from 20-60wt% of the total weight of the slag and aqueous liquid, optionally from 30- 50wt% and optionally from 30-40wt% of the total weight of the slag and aqueous liquid. [0024] Contacting the slag with the aqueous liquid may take place in a treatment composition-producing chamber. The treatment composition-producing chamber may be provided with an inlet for the aqueous liquid and an mlet for slag. As mentioned above, the treatment composition may be formed from a high-pH treatment composition. Reducing the pH of the high-pH treatment composition to produce the treatment composition may comprise contacting the high-pH treatment composition with a pH-reducing agent or with water. The pH-reducing agent may comprise an acid. The pH-reducing agent may comprise a gas, such as a gas comprising carbon dioxide. Reducing the pH of the pre-treatment composition to produce the treatment composition may comprise passing a gas (for example, a gas comprising carbon dioxide) through the treatment composition. Carbon dioxide reduces pH and produces carbonates that may precipitate. The use of carbon dioxide also facilitates carbon capture in the precipitated carbonates. Those skilled in the art will realise that a gas comprising carbon dioxide may comprise components other than carbon dioxide. If the pH-reducing agent comprises a gas, such as a gas comprising carbon dioxide, the pH-reducing agent may be provided as bubbles. The pH-reducing agent may be provided as bubbles, at least a portion of which have a diameter of no more than 500nm, optionally no more than 400nm, optionally no more than 300nm and optionally no more than 200nm.

[0025] Formation of the treatment composition from a pre- treatment composition may take place in the same chamber in which the pre-treatment composition is formed. Alternatively, the treatment composition may be formed in a different chamber. In this case, the method may comprise transferring pre-treatment composition from the pre-

treatment composition producing chamber to a pH-reducing chamber. The pH-reducing chamber may be provided with an inlet for a pH-reducing agent. The inlet for a pH- reducing agent may be located at or near a bottom of the pH-reducing chamber. The pH- reducing chamber may be a tower, for example.

[0026] Contacting the treatment composition having a pH of from 8 to 11 with the ferrous metal processing by-product may comprise agitating the treatment composition and/or ferrous metal processing by-product. Agitating the treatment composition and/or the ferrous metal processing by-product may optionally comprise contacting a gas with the treatment composition and/or ferrous metal processing by-product. Agitating the treatment composition and/or the ferrous metal processing by-product may optionally comprise introducing a gas into the treatment composition. Agitating the treatment composition and/or the ferrous metal processing by-product may comprise introducing a gas into the treatment composition and permitting the gas to rise through the treatment composition.

[0027] Contacting of the treatment composition having a pH of from 8 to 11 with the zinc- containing ferrous metal processing by-product may comprise generating a spray comprising the treatment composition. The method may comprise contacting the zinc- containing ferrous metal processing by-product with the spray. The weight% of the treatment composition may be at least 10wt% of the total weight of the pH treatment composition and the zine-containing ferrous metal processing by-product, optionally at least 20wt%, optionally at least 30wt%, optionally at least 40wt% and optionally at least 50wt% of the total weight of the treatment composition and the zinc-containing ferrous metal processing by-product. The weight% of the treatment composition may be on more than 80wt% of the total weight of the treatment composition and the zinc-containing ferrous metal processing by-product, optionally no more than 70wt%, optionally no more than 60wt% and optionally no more than 50wt% of the total weight of the treatment composition and the zmc-containmg ferrous metal processing by-product.

[0028] Contacting the treatment composition with the ferrous metal processing by-product may produce a slurry or suspension.

[0029] The pH of the slurry or suspension formed by contacting the treatment composition and the ferrous metal processing by-product is preferably maintained at a value of from 9-

11 and more preferably from 9.5 to 10.5 to ensure that the zinc dissolves in the liquid of the slurry or suspension. In this connection, the method may comprise monitoring the pH of the slurry or suspension, and adjusting the pH, dependent on the monitored pH.

[0030] The method may comprise monitoring the concentration of zinc in the zinc- enhanced solution. The method may comprise comparing the monitored concentration with a desired concentration. If the monitored concentration is sufficiently high (for example, if the concentration is at or near to the saturation concentration, then the zinc-enhanced solution may be removed for further treatment, for example, precipitation of a zinc salt.

[0031] The method may comprise separating the zinc-enhanced solution from the zinc- depleted ferrous metal processing by-product. Separating the zinc-depleted component from the zinc-enhanced component may comprise applying a magnetic field to the zinc- depleted component and the zinc-enhanced component. The zinc-depleted component may optionally comprise magnetic material, such as ferrous material. The zinc-enhanced component may also comprise magnetic material, but not as high a percentage as the zinc- depleted component. Separating the zinc-depleted component from the zinc-enhanced component may comprise using a density separation method. For example, a jig may be used to separate the zinc-enhanced component from the zinc-depleted component.

[0032] The method may comprise precipitating a zinc-containing material (such as a zinc- containing salt) from the zinc-enhanced solution. Precipitating a zinc salt from the zinc- enhanced solution may comprise one or more of adjusting the pH, heating the zinc- enhanced solution, cooling the zinc-enhanced solution, removing solvent from the zinc- enhanced solution, adding solvent to the zinc-enhanced solution, generating a counterion in the zinc-enhanced solution or adding a counterion to the zinc-enhanced solution. For example, the method may comprise contacting carbon dioxide with the zinc-enhanced solution.

[0033] Precipitation of the zinc salt may take place in a precipitation chamber. The method may therefore comprise moving the zinc-enhanced solution to a precipitation chamber.

[0034] Contacting the treatment composition with the ferrous metal processing by-product may take place in a zinc-removal chamber. The zinc-removal chamber may be provided with an inlet for aqueous liquid, for example. The zinc-removal chamber may be provided

with an inlet for a pH-adjusting agent, such as acid or alkali. The zinc-removal chamber may be provided with an outlet for the zinc-enhanced solution and may be provided with an outlet for the zinc-depleted ferrous metal processing by-product.

[0035] The method of the present invention provides a solid, zinc-depleted ferrous metal processing by-product, optionally in the form of particulate. The method may comprise agglomerating said zinc-depleted ferrous metal processing by-product, optionally into pellets. The pellets may be of any suitable size and shape. The mean greatest dimension of the pellets of the agglomerate composition may be at least 2mm, optionally at least 5mm and optionally at least 10mm. The mean greatest dimension may be up to 100mm, optionally up to 80mm, optionally up to 60mm, optionally up to 50mm and optionally up to 40mm. The mean greatest dimension may be from 10mm to 50mm, for example. The pellets of the agglomerate composition may be substantially spherical, in which case the mean diameter of the pellets of the agglomerate composition may be at least 2mm, optionally at least 5mm and optionally at least 10mm. The mean diameter may be up to 100mm, optionally up to 80mm, optionally up to 60mm, optionally up to 50mm and optionally up to 40mm. The mean diameter may be from 10mm to 50mm, for example. Pellets of such size have been found to be advantageous.

[0036] The ferrous metal processing by-product may be, or be derived from, steel byproduct, such as the so-called “steel dust” (for example, by-product dust collected from the off gases of steel making converters or furnaces, such as oxygen blown converters or electric arc furnaces, and any heavier drop-out material).

[0037] The ferrous metal processing by-product may comprise iron. The ferrous metal processing by-product (prior to treatment to remove zinc) may comprise at least 5wt% iron, optionally at least 10wt% iron, optionally at least 15wt% iron and optionally at least 20wt% iron. The pre-treatment ferrous metal processing by-product may comprise no more than 80wt% iron, optionally no more than 70wt% iron, optionally no more than 60wt% iron, optionally no more than 50wt% iron, optionally no more than 40wt% iron, optionally no more than 35wt% iron, optionally no more than 30wt% iron and optionally no more than 25wt% iron. The wt% above are based on the weight of the ferrous metal processing by-

product. At least some of the iron may be in the form of an iron oxide, such as Fe^CF or FesC . At least some of the iron may be in the form of iron metal i.e. elemental iron.

[0038] The pre-treatment ferrous metal processing by-product may comprise at least 30wt% iron, optionally at least 40wt% iron and optionally at least 50wt% iron.

[0039] The pre-treatment ferrous metal processing by-product may comprise no more than 40wt% zinc, optionally no more than 35wt% zinc, optionally no more than 30wt% zinc, optionally no more than 25wt% zinc and optionally no more than 20wt% zinc. Such relatively high levels of zinc may be found, for example, in by-product generated by electric arc furnace steel making.

[0040] The particulate by-product may comprise at least 5wt% zinc, optionally at least 10wt% zinc, optionally at least 15wt% zinc and optionally at least 20wt% zinc. The zinc may be in the form of zinc oxide.

[0041] The particulate by-product may comprise at least 0.5wt% zinc, optionally at least 1.0wt% zinc and optionally at least 1.5wt% zinc. The particulate may comprise no more than 5wt% zinc, optionally no more than 4wt% zinc, optionally no more than 3wt% zinc, optionally no more than 2.0wt% and optionally no more than 1.5wt% zinc. Such relatively low levels of zinc may, for example, be generated by blown oxygen steel making.

[0042] The particulate may optionally comprise one or more of chromium, lead, aluminium, manganese and calcium.

[0043] The method of the present invention may be used to reduce the zinc content of a ferrous metal processing by-product to a level sufficiently low to allow the ferrous metal processing by-product to be used in an iron or steel-related process, such as in a blast furnace, as opposed to being treated as by-product. For example, sufficient zinc may be removed from blown oxygen convertor by-product to facilitate use of the zinc-depleted byproduct in a blast furnace.

[0044] The method of the present invention may provide a zinc-depleted component and a zinc-enhanced component. The method may comprise separating the zinc-depleted component from the zinc-enhanced component.

[0045] The applicant has found that contacting of the treatment liquid with the ferrous metal processing by-product may generate hydrogen gas (H2). The method of the present

invention may therefore comprise collecting hydrogen gas. Collecting hydrogen gas may comprise storing hydrogen gas, optionally in a receptacle for the storage of hydrogen. Collecting hydrogen gas may comprise increasing the concentration of hydrogen in a gas generated by contacting the treatment liquid with the ferrous metal processing by-product, and/or removing hydrogen gas from the gas generated by contacting the treatment liquid with the ferrous metal processing by-product. The method may comprise storing said gas after increasing the concentration of hydrogen in the gas generated by contacting the treatment liquid with the ferrous metal processing by-product and/or removing hydrogen gas from the gas generated by contacting the treatment liquid with the ferrous metal processing by-product. Collecting hydrogen gas may comprise contacting a gas generated by contacting the treatment liquid with the ferrous metal processing by-product with a gas treatment means for increasing the concentration of hydrogen in the gas or for removing the hydrogen from the gas. The method may comprise purifying the hydrogen gas.

[0046] The applicant has found that a pH of 8 is particularly effective at producing hydrogen. The applicant has found that a pH of 9 or 9.5 is effective at both removing zinc from the by-product and generating hydrogen.

[0047] According to a second aspect of the invention there is also provided an apparatus for the treatment of ferrous metal processing by-product comprising zinc, the apparatus comprising:

(i) A treatment composition-forming chamber;

(li) A zinc-removal chamber in fluid communication with, and configured to receive treatment composition from, the treatment composition-forming chamber; and

(iii) A precipitation chamber in fluid communication with, and configured to receive zinc-enhanced solution from, the zinc-removal chamber.

[0048] The apparatus of the second aspect of the present invention may comprise an agglomerator in communication with, and configured to receive zinc-depleted ferrous metal processing by-product from, the zinc-removal chamber.

[0049] The apparatus may comprise a pH-reducing chamber in fluid communication with, and configured to receive a high-pH treatment composition from, the treatment composition-forming chamber, the pH-reducing chamber being in fluid communication with, and configured to deliver treatment composition to, the zinc-removal chamber. The pH-reducing chamber, if present, is used to reduce the pH of a high-pH treatment composition formed in the treatment composition-forming chamber, and to deliver a treatment composition with a reduced pH comparted to the high-pH treatment composition to the zinc removal chamber. The pH-reducing chamber may comprise one or more inlets for the introduction of a gas, such as a gas comprising carbon dioxide, such as air. One or more of said inlets may be located at or proximate to a bottom of the pH-reducing chamber. The pH-reducing chamber may comprise a tower.

[0050] The apparatus may comprise a hydrogen collector. The hydrogen collector may comprise a receptacle for the storage of hydrogen gas. The hydrogen collector may comprise a means for removing hydrogen from a gas generated by contacting the treatment composition with the ferrous metal processing by-product. The hydrogen collector may comprise a means for increasing the concentration of hydrogen in a gas generated by contacting the treatment composition with the ferrous metal processing by-product. The receptacle for the storage of hydrogen gas may be configured to receive gas from the means for removing hydrogen and/or the means for increasing the concentration of hydrogen.

[0051] The zinc-removal chamber may be provided with one or more spray outlets for producing a spray of pH-reduced treatment composition. The one or more spray outlets may be provided at or near a top of the zinc-removal chamber.

[0052] According to a third aspect of the present invention, there is provided a method of treating ferrous metal processing by-product, the method comprising:

(a) contacting a treatment composition with ferrous metal processing byproduct, thereby producing hydrogen, the treatment composition having a pH of from 8 to 11, and having been produced by contacting an aqueous liquid with slag; and

(b) collecting the hydrogen gas.

[0053] The method of the third aspect of the present invention may comprise one or more features of the method of the first aspect of the present invention. For example, collecting hydrogen gas may comprise storing hydrogen gas.

[0054] The method may comprise producing the treatment composition by contacting an aqueous liquid with slag, and contacting the treatment composition with ferrous metal processing by-product. The method may comprise producing the treatment composition by contacting an aqueous liquid with slag, and subsequently contacting the treatment composition with ferrous metal processing by-product.

[0055] The method may comprise producing the treatment composition in the presence of ferrous metal processing by-product. The ferrous metal processing by-product may therefore be in contact with the treatment composition as the treatment composition is being made.

[0056] Producing a treatment composition having a pH of from 8 to 11 may take place in the presence of the ferrous metal processing by-product. For example, producing the treatment composition may comprise reducing the pH of a pre-treatment composition in the presence of the ferrous metal processing by-product.

[0057] In accordance with a fourth aspect of the present invention, there is provided an apparatus for treating ferrous metal processing by-product, the method comprising:

(i) a treatment composition-forming chamber;

(ii) a reaction chamber in fluid communication with, and configured to receive treatment composition from, the treatment composition-forming chamber; and

(iii) a hydrogen collector for collecting hydrogen released by contacting treatment composition with ferrous metal processing by-product.

[0058] The apparatus of the fourth aspect of the present invention may comprise one or more features of the apparatus of the second aspect of the present invention. For example, the reaction chamber may comprise one or more features of the zinc-removal chamber of the apparatus of the second aspect of the present invention. For example, the hydrogen

collector may comprise one or more features of the hydrogen collector described above in relation to the apparatus of the second aspect of the invention.

[0059] In the statements above relating to the first to the fourth aspects of the present invention, reference is made to ferrous metal processing by-product. Such by-products are often seen as waste products (to the extent that such by-products are often not wanted or desired), and therefore herein reference to “by-product” also includes reference to “waste” and may be used interchangeably.

[0060] It will, of course, be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the first aspect of the invention may incorporate any of the features described with reference to the apparatus of the second aspect of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0061] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0062] Figure 1 shows a schematic representation of an example of an embodiment of an apparatus in accordance with the second and fourth aspects of the present invention; and [0063] Figure 2 shows a schematic representation of a further example of an embodiment of an apparatus in accordance with the second and fourth aspects of the present invention.

DETAILED DESCRIPTION

[0064] An example of a method of treating ferrous metal processing by-product comprising zinc will now be described by way of example only by reference to Figure 1. In this case, the ferrous metal processing by-product is basic oxygen steel processing (BOSP) by-product, which comprises various iron oxides (including iron (II) oxide and iron (III) oxide), metallic iron and zinc. The method of treating zinc-containing ferrous metal processing by-product comprises contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11, and contacting the treatment

composition with ferrous metal processing by-product comprising zinc, thereby producing a zinc-enhanced solution and a zinc-depleted ferrous metal processing by-product. In the present example, treatment composition having a pH of from 8 to 11 is made by producing a high-pH treatment composition having a pH of about 13 by contacting water with the slag, and then reducing the pH of the high-pH treatment composition to a value of 8-11 . In this connection, an apparatus denoted generally by reference numeral 1 is provided. The apparatus 1 comprises a treatment composition-producing chamber 2, a pH-reducing chamber 3, a zinc-removal chamber 4, a precipitating chamber 5, a means for treating gas 6 and a receptacle 7 for the storage of gas configured to receive gas from the means for treating gas. Slag from a blast furnace is deposited into the treatment compositionproducing chamber 2. Recovered rain water is introduced into the treatment compositionproducing chamber 2, and the slag and rain water are agitated using a gas introduced into aeration ports (now shown) located towards the bottom of the treatment compositionproducing chamber. The pH increases as the rain water and slag are agitated. The pH of the liquid is monitored, with a desired pH of the high-pH treatment composition being about 13. If the pH is lower than 13 and does not seem to be rising sufficiently, then more slag is added. If the pH exceeds 13, then more rain water is added.

[0065] Once the correct pH has been reached, the high-pH treatment composition is transferred to the pH-reducing chamber 3. Air is introduced into aeration ports (not shown) located at or near the bottom of the pH-reducing chamber 3. The carbon dioxide in the air reacts with calcium in the high-pH treatment composition to produce calcium carbonate, thereby facilitating carbon capture by removing carbon dioxide from the air. The carbon dioxide also reduces the pH of the treatment composition to the desired value of 8-11.

[0066] The pH of the treatment composition in the pH-reducing chamber is monitored. Once the pH reaches the desired value of 8-11, the treatment composition is transferred from the pH-reducing chamber to the zinc-reducing chamber 4. Ferrous metal processing by-product comprising zinc in the form of basic oxygen steel processing by-product is present in the zinc-reducing chamber 4. The relative weights of steel processing by-product and treatment composition are 60:40wt%. Air is introduced into aeration ports (not shown) located at or near the bottom of the zinc-reducing chamber. Zinc present in the steel

processing by-product dissolves in the alkali treatment composition, depleting the steel processing by-product of zinc, and enhancing the treatment composition with zinc. Those skilled in the art will realise that not all of the zinc need be removed from the steel processing by-product. The pH of the by-product: treatment composition slurry is monitored to ensure that it stays within the desired range of 8-11. If the pH drops below 8, then an alkali may be added to increase the pH. If the pH drops below 8, then the solubility of zinc in the treatment composition is significantly reduced.

[0067] The concentration of zinc ions in the slurry is monitored. If the concentration is at or above a pre-determined level, then the zinc-enhanced liquid is transferred to the precipitating chamber 5. If the concentration of zinc ions has not reached the predetermined level and is not increasing, then more steel processing by-product is added to the slurry.

[0068] In the precipitating chamber 5, water is added to the zinc-enhanced liquid to reduce the pH. As the pH is reduced, the solubility of zinc reduces and zinc salts precipitate from the zinc-enhanced liquid. The precipitated zinc salts may be used as appropriate.

[0069] The zinc-depleted ferrous metal processing by-product is removed from the zinc- reducing chamber 4 and dried. The zinc-depleted ferrous metal processing by-product is then pelletised, optionally for use in a blast furnace.

[0070] The applicant has discovered that contacting the treatment composition with the ferrous metal processing by-product produces hydrogen gas. Without wishing to be bound by theory, the applicant understands that oxidation of iron (possibly metallic iron or iron (II)) present in the by-product in the alkaline conditions leads to the formation of hydrogen gas. Gas comprising the liberated hydrogen contacts a means 6 for removing hydrogen from the gas. In this case, the means 6 for removing hydrogen from the gas removes hydrogen from the gas, the hydrogen being transferred to the receptacle 7 for receiving a gas comprising hydrogen. The receptacle 7 is suitable for storing hydrogen.

[0071] A further example of a method of treating zinc-containing by-product will now be described by way of example only by reference to Figure 2. The method of treating zinc- containing ferrous metal processing by-product comprises contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11, and contacting

the treatment composition with ferrous metal processing by-product comprising zinc, thereby producing a zinc-enhanced solution and a zinc-depleted ferrous metal processing by-product. In the present example and in contrast to the method described above in relation to Figure 1, treatment composition having a pH of from 9.5 to 11 is not made by the sequential production of a high-pH treatment composition having a pH of about 13 by contacting water with the slag, and then reducing the pH of the high-pH treatment composition to a value of 8-11. In the present example, the treatment composition having a pH of 8-11 is made by contacting an aqueous liquid (in this case, recovered rain water) with slag and contacting a pH-reducing agent with the aqueous liquid and slag. In this connection, an apparatus denoted generally by reference numeral 101 is provided. The apparatus 101 comprises a treatment composition-producing chamber 102, a zinc-removal chamber 104, a precipitating chamber 105, a gas treatment means 106 and a receptacle 107 configured to receive gas from the gas treatment means 106. Slag from a blast furnace is deposited into a treatment composition-producing chamber 102. Recovered rain water is introduced into the treatment composition-producing chamber 102, and the slag and rain water are agitated using a gas (in this case, air) introduced into aeration ports (now shown) located towards the bottom of the treatment composition-producing chamber. The pH increases as the rain water and slag are agitated. The air comprises carbon dioxide. The carbon dioxide acts as a pH-reducing agent, reducing the pH of the treatment composition. Furthermore, the carbon dioxide reacts with calcium-containing compounds in the slag to form calcium carbonate, which precipitates from solution. The pH of the liquid is monitored, with a desired pH of the treatment composition being 8-11.

[0072] Once the correct pH has been reached, the treatment composition is transferred from the treatment composition-producing chamber 102 to the zinc-reducing chamber 104. Ferrous metal processing by-product comprising zinc in the form of basic oxygen steel processing by-product is present in the zinc-reducing chamber 104. The relative weights of steel processing by-product and treatment composition are 60:40wt%. Air is introduced into aeration ports (not shown) located at or near the bottom of the zinc-reducing chamber. Zinc present in the steel processing by-product dissolves in the alkali treatment composition, depleting the steel processing by-product of zinc, and enhancing the treatment

composition with zinc. Those skilled in the art will realise that not all of the zinc need be removed from the steel processing by-product. The pH of the by-product: treatment composition slurry is monitored to ensure that it stays within the desired range of 8-11. If the pH drops below 8, then an alkali may be added to increase the pH. If the pH drops below 9.5, then the solubility of zinc in the treatment composition is significantly reduced. However, at pH values lower than 9.5, hydrogen generation is improved.

[0073] The concentration of zinc ions in the slurry is monitored. If the concentration is at a pre-determined level with respect to the concentration of zinc ions, then the zinc- enhanced liquid is transferred to the precipitating chamber 105. If the concentration of zinc ions has not reached the pre-determined level and is not increasing, then more ferrous metal processing by-product is added to the slurry.

[0074] In the precipitating chamber 105, water is added to the zinc-enhanced liquid to reduce the pH. As the pH is reduced, the solubility of zinc reduces and zinc salts precipitate from the zinc-enhanced liquid.

[0075] The zinc-depleted ferrous metal processing by-product is removed from the zinc- reducing chamber 104 and dried. The zinc-depleted ferrous metal processing by-product is then pelletised, optionally for use in a blast furnace.

[0076] As mentioned above, the applicant has discovered that contacting the treatment composition with the ferrous metal processing by-product produces hydrogen gas. Without wishing to be bound by theory, the applicant understands that oxidation of iron (possibly metallic iron or iron (II)) present in the by-product in the alkaline conditions leads to the formation of hydrogen gas. Gas comprising the liberated hydrogen contacts a means 106 for treating gas. In this instance, the means 106 comprises a means for removing hydrogen from the gas. In this case, the means 106 for removing hydrogen from the gas removes hydrogen from the gas, the hydrogen being transferred to the receptacle 107 for receiving a gas comprising hydrogen. The receptacle 107 is suitable for storing hydrogen.

[0077] Several embodiments of examples in accordance with the present invention will now be described by way of example only. A pre-treatment composition was made by gradually adding BOS slag to deionized water until the pH stopped increasing, pH being determined using a Mettler Toledo F2 pH/mV. In this connection, aliquots of about 5g of

BOS slag were added to 500 mL deionized water, and stirred for 5 minutes. 5g aliquots were added until the pH stopped rising. The pH evened out at pH 11.8 after the addition of 75.5 g of slag. The slag residue was removed using a vacuum filter pump. The pH of the pre-treatment composition could then be reduced to form a treatment composition.

[0078] In each of the Comparative Examples and Examples below, laser absorption spectroscopy was used to identify a gas, in particular, whether hydrogen gas was present. Samples of the generated gas were collected and analysed using infrared spectroscopy to determine purity/composition of the gas.

Comparative Example 1.

[0079] 10g of reduced iron powder was added to a 100 mL double-necked flask. The flask was then purged with nitrogen for 10 minutes. 90 mL of a treatment composition of pH 11 was then added via super-seal to the flask. An upturned cylinder was used to measure the gas produced.

Comparative Example 2

[0080] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 10 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10 g of reduced iron powder was added. An upturned cylinder was used to measure the gas produced.

Comparative Example 3

[0081] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 9 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10 g of reduced iron powder was added. An upturned cylinder was used to measure the gas produced.

Comparative Example 4

[0082] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 8 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10 g of reduced iron powder was added. An upturned cylinder was used to measure the gas produced.

[0083] In each of Comparative Examples 1 to 4 above, hydrogen gas was generated and collected.

Example 1

[0084] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 10 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS dust was added. An upturned cylinder was used to collect and measure the gas produced.

Example 2

[0085] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 9 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS dust was added. An upturned cylinder was used to collect and measure the gas produced.

Example 3

[0086] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 8 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS dust was added. An upturned cylinder was used to collect and measure the gas produced.

Example 4

[0087] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 11 was reached. After purging the

flask for 1.5 hours with nitrogen gas in a round bottom flask, 1 Og BOS dust was added. An upturned cylinder was used to collect and measure the gas produced.

Example 5

[0088] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 10 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS slurry was added. An upturned cylinder was used to measure the gas produced.

Example 6

[0089] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 11 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS slurry was added. An upturned cylinder was used to measure the gas produced.

Example 7

[0090] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 9 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS slurry was added. An upturned cylinder was used to measure the gas produced.

Example 8

[0091] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 8 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 10g BOS slurry was added. An upturned cylinder was used to measure the gas produced.

Example 9

[0092] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 11 was reached. After purging the flask for 1 .5 hours with nitrogen gas in a round bottom flask, 3g BOS slurry and 3g BOS dust were added. An upturned cylinder was used to measure the gas produced.

Example 10

[0093] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 10 was reached. After purging the flask for 1.5 hours with nitrogen gas in a round bottom flask, 3g BOS slurry and 3g BOS dust were added. An upturned cylinder was used to measure the gas produced.

Example 11

[0094] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 9 was reached. After purging the flask for 1 .5 hours with nitrogen gas in a round bottom flask, 3g BOS slurry and 3g BOS dust were added. An upturned cylinder was used to measure the gas produced.

Example 12

[0095] Air comprising carbon dioxide was passed through the pre-treatment composition described above in a round bottom flask until a pH of 8 was reached. After purging the flask for 1 .5 hours with nitrogen gas in a round bottom flask, 3g BOS slurry and 3g BOS dust were added. An upturned cylinder was used to measure the gas produced.

[0096] In each of Examples 1 to 12 above, the gas was collected and found to be 90-98% hydrogen, with the remainder being predominantly water vapour. A pH of 8 was found to be particularly effective at generating hydrogen gas.

[0097] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0098] The examples above describe the use of the method of the invention to remove zinc from by-product from the basic oxygen steelmaking process. Those skilled in the art will realise that other types of ferrous metal processing by-product comprising zinc may be used.

[0099] The examples above demonstrate the use of carbon dioxide to reduce the pH of the pre-treatment composition. Those skilled in the art will realise that other pH-reducing agents may be used.

[00100] The examples above demonstrate the generation of hydrogen gas when a treatment composition is contacted with a ferrous metal processing by-product comprising zinc. Those skilled in the art will realise that the presence of zinc is not necessary to generate hydrogen gas.

[00101] The examples above illustrate the making of the treatment composition and the subsequent contacting of the treatment composition with the ferrous material to be treated. Those skilled in the art will appreciate that this need not be the case. For example, the ferrous material to be treated may be present, and in contact with, the treatment composition as the treatment composition is made.

[00102] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A method of treating ferrous metal processing by-product comprising zinc, the method comprising: contacting a treatment composition with ferrous metal processing by-product comprising zinc, thereby producing a zinc-enhanced solution and a zinc-depleted ferrous metal processing by-product, the treatment composition having a pH of from 8 to 11, the treatment composition having been produced by contacting an aqueous liquid with slag.

2. The method of claim 1 in which the treatment composition has a pH of from 9.5 to 11.

3. The method of claim 1 or claim 2 in which the slag comprises ferrous slag.

4. The method of any preceding claim comprising producing the treatment composition in the presence of the ferrous metal processing by-product comprising zinc.

5. The method of claim 4, wherein producing the treatment composition in the presence of the ferrous metal processing by-product comprising zinc comprises reducing the pH of a pre-treatment composition in the presence of the ferrous metal processing by-product comprising zinc, optionally using a pH-reducing agent, such as carbon dioxide.

6. The method of any preceding claim, comprising producing the treatment composition having a pH of from 8 to 11 by contacting an aqueous liquid with slag, and contacting the treatment composition with the ferrous metal processing by-product comprising zinc.

7. The method of claim 6 wherein contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11 comprises contacting an aqueous liquid with slag to produce a pre-treatment composition and reducing the pH of the pretreatment composition using a pH-reducing agent to produce the treatment composition having a pH of from 8 to 11.

8. The method of claim 7, wherein the pre-treatment composition has a pH of at least 11 and of no more than 13. The method of any of claims 6 to 8, wherein contacting an aqueous liquid with slag to produce a treatment composition having a pH of from 8 to 11 comprises contacting the aqueous liquid with slag in the presence of a pH-reducing agent. The method of any of claims 7 to 9, wherein the pH-reducing agent comprises a gas. The method of claim 10 wherein the gas comprises carbon dioxide. The method of any preceding claim wherein the amount of aqueous liquid is at least 20wt% of the total weight of the slag and aqueous liquid. The method of any preceding claim wherein the amount of aqueous liquid is no more than 80wt% of the total weight of the slag and aqueous liquid. The method of any preceding claim wherein the amount of aqueous liquid is from 20 to 60wt% of the total weight of the slag and aqueous liquid. The method of any preceding claim, comprising agitating the treatment composition and/or ferrous metal processing by-product. The method of claim 15, wherein agitating the treatment composition and/or the ferrous metal processing by-product comprises contacting a gas with the treatment composition and/or ferrous metal processing by-product. The method of any preceding claim, wherein contacting the treatment composition with the ferrous metal processing by-product produces a slurry or suspension, and the pH of the slurry or suspension is maintained at a value of from 8-11. The method of any preceding claim, comprising monitoring the concentration of zinc in the zinc-enhanced solution, and comparing the monitored concentration with a desired concentration. The method of any preceding claim, comprising separating the zinc-enhanced solution from the zinc-depleted ferrous metal processing by-product. The method of any preceding claim, comprising precipitating a zinc-containing material (such as a zinc-containing salt) from the zinc-enhanced solution. 21 The method of any preceding claim, comprising agglomerating said zinc-depleted ferrous metal processing by-product.

22. The method of any preceding claim, wherein the ferrous metal processing by-product is, or is derived from, steel dust.

23. The method of any preceding claim, wherein the pre-treatment ferrous metal processing by-product comprises at least 5wt% iron, and optionally no more than 60wt% iron.

24. The method of any preceding claim, wherein the pre-treatment ferrous metal processing by-product comprises from 5 to 40wt% zinc or from 0.5-2.0wt% zinc.

25. The method of any preceding claim, wherein contacting the treatment composition with ferrous metal processing by-product comprising zinc produces hydrogen gas, and the method comprises collecting hydrogen gas.

26. The method of claim 25 wherein collecting hydrogen gas comprises one or more of (i) increasing the concentration of hydrogen in a gas generated by contacting the treatment liquid with the ferrous metal processing by-product, (ii) removing hydrogen gas from the gas generated by contacting the treatment liquid with the ferrous metal processing by-product and (iii) storing hydrogen gas.

27. An apparatus for the treatment of ferrous metal processing by-product comprising zinc, the apparatus comprising:

(i) A treatment composition-forming chamber;

(ii) A zinc-removal chamber in fluid communication with, and configured to receive treatment composition from, the treatment composition-forming chamber; and

28. The apparatus of claim 27, comprising a pH-reducing chamber in fluid communication with, and configured to receive a high-pH treatment composition from, the treatment composition-forming chamber, the pH-reducing chamber being in fluid communication with, and configured to deliver treatment composition to, the zinc-removal chamber.

29. The apparatus of claim 27 or claim 28, comprising a hydrogen collector for collecting hydrogen released by contacting the treatment composition with ferrous metal processing by-product, the hydrogen collector optionally comprising (i) a means for removing hydrogen from a gas generated by contacting the treatment composition with the ferrous metal processing by-product, (ii) a means for increasing the concentration of hydrogen in a gas generated by contacting the treatment composition with the ferrous metal processing by-product, and/or (iii) a receptacle for the storage of hydrogen gas, the receptacle being configured to receive gas from the means for removing hydrogen and/or the means for increasing the concentration of hydrogen.

30. A method of treating ferrous metal processing by-product, the method comprising:

(a) contacting a treatment composition with ferrous metal processing by-product, thereby producing hydrogen, the treatment composition having a pH of from 8 to 11, and having been produced by contacting an aqueous liquid with slag; and

(b) collecting the hydrogen gas.

31. An apparatus for treating ferrous metal processing by-product, the method comprising:

(i) a treatment composition-forming chamber;